The receptor on murine T cells that recognizes antigen presented by a specific Ia bearing presenting cell is being studied in order to understand the mechanism of specific immune activation. The approaches used are based on the isolation, identification, characterization and purification of the components of this receptor. In addition biochemical studies are aimed at identifying the mechanisms whereby occupancy of this receptor transduces a signal to activate the T cell. Using an antigen specific T cell hybridoma that recognizes a fragment of pigeon cytochrome C we have demonstrated that occupancy of the receptor in a manner that leads to cell activation results in the phosphorylation of a protein specifically associated with the T cell receptor. Furthermore, the interaction of T cell, antigen and presenting cells leads to increased levels of phosphorylated phosphatidylinositol. In addition enhanced breakdown of these phosphorylated lipids leads to the production of water soluble inositol phosphates via a phosphodiesterase. By immunoprecipitating the antigen receptor with a monoclonal antibody directed against the unique binding site of the receptor, we have identified a specific set of proteins which are non covalently associated with the clonotypic Alpha and Beta chains, that alone previously defined the receptor. Four unique proteins, termed Gamma, Delta, Epsilon and Zeta comprise this complex. They are all expressed on the surface of the T cell and are most likely all transmembrane proteins and one is a homodimer. Thus the minimum complex that defines the T cell antigen receptor contains seven chains including the Alpha-Beta dimer that recognizes specific antigen.